Environmental problems are frequently related to waste and toxic organic pollutants discharged in water bodies. Most of the colored effluents found in contaminated waters consist of organic dyes from textiles, dyestuff and dyeing industries. Sulfonated azo dyes and phenazine dyes are the most common compounds used in fabric factories. Conventional waste water treatments like flocculation, activated carbon adsorption and bioremediation have been shown to be ineffective in the remediation of organic dyes mainly because of the high solubility of these contaminants in water, besides, these processes produce large quantities of sludge. Therefore, photocatalysis can be considered an attractive alternative route to degrade and destroy contaminants. Some advantages of the photocatalytic approach include a quick oxidation of the pollutant molecules, lack of production of polycyclic products and final degradation of pollutants in the ppb range.
The photo-catalytic destruction of organic dyes is a process that combines catalysis with solar radiation-based technologies. In this regard, semiconductors quantum dots (QDs) absorb light of energy more than or equal to its band-gap, a process that generates electron and holes, and further free-radicals that can be used to oxidize the contaminants.
Quantum dots exhibit higher surface-area to volume ratio than their bulk counterparts and thus allow for greater photon absorption on the photocatalyst surface. Also, the higher band gap energy observed in quantum dots in comparison to the bulk produces a higher redox potential in the system. Previous studies have synthesized Cd-based and Zn-based QDs with photocatalytic properties for the degradation of organic pollutants under UV light irradiation; however, the main limitation in these works has been the recovery of these nanomaterials after the expected photo-catalytic reactions have taken place. The small size of nanoparticles avoids their recovery by the use of traditional techniques such as precipitation, centrifugation among others, so that, the use and reuse of these materials in high volumes of contaminated water is not a viable process.
On the other hand, bi-functional nanostructures provide the possibility to obtain materials with photocatalytic and magnetic properties, which can facilitate their recuperation and posterior reuse. Fluorescent magnetic nanocomposites based on Fe2O3 and CdTe have been synthesized by Yan et al. (included herein by reference), however, their photocatalytic properties were not studied.